1. Field of the Invention
This invention relates to flexible polyurethane foams. More particularly, it relates to flexible polyurethane foams having reduced smoke generation when in contact with a flame and having flame retardant properties, and a process of making the same.
2. Description of the Prior Art
Heretofore, polyurethane foams have been produced by reacting, under foaming conditions, a compound containing a plurality of active hydrogen atoms with a polyisocyanate. The resulting foams often have no flame resistance and release smoke in large amounts when in contact with a flame.
It has also been known to produce flame resistance polyurethane foams by incorporation therein of a flame retarding compound which contains phosphorus or halogen atoms. While it is thus possible to reduce the flammability of the foamed polyurethane, the resultant product still has disadvantages such as (1) deterioration of the flame retarding property caused by bleeding out or evaporation of the flame retarding compound; (2) an adverse effect of the compound on some of the physical properties of the foamed product; and (3) occurrence of scorching. Another serious defect encountered when the foamed product is on fire, is the generation of a large amount of smoke as well as poisonous gases containing halogen or phosphorus compounds.
It has also been proposed to reduce the flammability and the amount of smoke generated by polyurethane foams without incorporation of a flame retarding compound. In these processes, for example, there is used a polyisocyanate compound having a biuret linkage or a compound having an isocyanurate ring. The resultant products are improved in most of the above-mentioned properties, but their structure consists of closed cells. Consequently, in order to prevent collapse of the foam, the structure must be changed to an open cell by unpractical methods such as the mechanical crushing of the cells. As a result, a fully satisfactory technique for rendering polyurethane foams fire retardant and for reducing the amount of smoke generated by the foams when in contact with a flame is needed.